1. Field of the Invention
This invention relates to high Young's modulus materials having high hardness and toughness and excellent wear resistance and capable of working in a high accuracy which are suitable as a material for cold working tools used under severer conditions as well as machine structural members requiring high regidity. And also, the invention relates to surface-coated tool members provided with a hard coating layer having a Young's modulus of not less than 24,000 kgf/mm.sup.2.
2. Description of the Related Art
Heretofore, super-hard materials (or cemented carbides) having a high Young's modulus have been used in cold working tools requiring a high accuracy such as punch for fine blanking, dies and the like.
On the other hand, high-alloying and high speed tool steels have been used in cold working tool made from molten steel material.
As a machine structural member requiring a high rigidity, there were used steel materials for machine structure by subjecting them to a heat treatment such as quenching, tempering or the like or a surface improving treatment such as carburizing, carbo-nitriding, nitriding or the like.
In punch, dies and the like for cold punching or cold forging, a coating layer of TiN, TiC or the like is formed on the surface of the substrate by a process such as PVD, CVD or the like for improving the service life.
For, example, when a hard coating layer such as TiN is formed on the surface of the substrate, the seizure or baking is prevented because TiN is less in the affinity with the steel material and is hard. And also, the working can smoothly be conducted because TiN is excellent in the abrasion resistance and the service life of the tool can be prolonged.
However, when a super-hard material is used in the cold working tool, the toughness is poor as compared with that of an iron series tool material, and also the cutting is not conducted in the working into a tool and the grinding becomes difficult.
In the high-alloying high-speed tool steel, the Young's modulus is 25000 kgf /mm.sup.2 at most. Therefore, if the alloying is further increased, macro-carbide crystal precipitates to lower the toughness and also the hot workability and the cutting and grinding in the working into tool degrade.
In the machine structural steel, the Young's modulus is 21,000 kgf/mm2 at most. Particularly, when the substrate requires high rigidity, the above steel is lacking in the Young's modulus, so that the thickness of the substrate is increased for compensating the Young's modulus and consequently the weight reduction of the tool member can not be attained.
When the working such as punching or the like is conducted with a tool having a coating layer in its surface, the substrate of the tool is deformed in the working, whereby the coating layer is subjected to strains. As a result, the coating layer is peeled off from the surface of the substrate or cracks are produced in the coating layer to finally bring about the breakage of the substrate.
Therefore, it is desired to develop high Young's modulus materials capable of reducing or solving the above problems as well as tool members provided therewith.